1. Field of the Invention
This invention relates to the field of dripless caulk guns, and to caulk guns having no barrel for supporting the caulk tube.
2. Description of Related Art
Caulk guns are used for dispensing and applying caulk and adhesive. Caulk is used by building contractors and homeowners for sealing windows and doors, particularly as a means of weatherproofing. Adhesive is used by craftspersons for adhering materials, typically wood. One industry convention for dispensing caulk and adhesive comprises a caulk gun in combination with a plastic or cardboard cylindrical canister or tube which is filled with caulk or adhesive. One end of the canister is provided with a nipple or nozzle for dispensing the caulk. Another end of the canister is provided with a drive plate (a movable end plate within the caulk tube) that rides along an interior surface of the canister and pushes against the caulk or adhesive so as to dispense it through the nipple. Hereinafter, reference will be made to caulk and caulk tubes, but it should be noted that the reference is intended to encompass both caulk and adhesives.
Prior art caulk guns provide a body that supports the caulk canister, a trigger and a plunger mechanism including a piston. Some caulk guns provide a ratchet and pawl arrangement wherein the trigger may be squeezed to advance the plunger and, as the trigger is released, the pawl clicks backward along one or more notches in the plunger so that when the trigger is squeezed again it advances the plunger from its previous position. With the ratchet and pawl engaged, the plunger is not free to move backwards. To release the plunger and move it back from the canister, the plunger must be rotated so as to disengage the pawl from the notches in the plunger, thereby permitting the plunger to move freely backwards.
Another type of caulk gun, referred to herein as a bias-spring drive system, is shown in Chang, U.S. Pat. No. 4,081,112. Chang discloses a biased "plunger drive grip" that grabs a plunger rod when it is canted by a trigger. Further motion of the trigger moves the drive grip and plunger against the caulk gun for dispensing caulk. A second trigger releases the drive grip so the plunger can move back to take pressure off the caulk tube to prevent continued dripping of caulk. Thus, the caulk gun of Chang would drip excess caulk until the second trigger is operated. However, even after the second trigger is actuated, some caulk will drip from the caulk gun because the drive plate in the caulk tube will maintain some pressure against the caulk in the canister, which pressure will be proportional to the frictional resistance of the drive plate against the interior walls of the caulk canister.
Prior art caulk guns included the aforementioned body that receives and supports the caulk canister. The body generally comprises a frame or cut-away barrel that extends from a proximal end near the trigger to a distal end. Frames generally comprise two or more stringers that extend from a stationary back plate connected to the handle and trigger assembly up to a cup-shaped front plate with a U-shaped cutout for the nozzle. In the case of the barrel shaped body, the barrel comprises an open semi-tube that receives and cradles the caulk canister between a back plate and a cup-shaped front plate. Generally, the back plate is recessed to receive a back end of the caulk canister while the canister's front end is dropped into position.
Several problems with prior art caulk guns are readily apparent to those skilled in the art. First, most prior art caulk guns operate by pushing a plunger against a drive plate inside the caulk tube thereby building up pressure within the caulk tube itself. Even after the trigger mechanism has been released, the caulk tube continues to slowly dispense caulk through the nozzle because of internal pressure in the caulk tube. Attempts to provide dripless caulk guns have achieved only partial success because all prior art attempts merely relieved the pressure of the plunger mechanism against the drive plate of the caulk tube. None of the prior art caulk guns provide any way of relieving the pressure of the drive plate against the caulk in the caulk tube.
Furthermore, prior art systems for holding the caulk tube in the gun had several disadvantages. The tolerance required between the plates, in order to allow the caulk tube to be loaded in the caulk gun, allowed an undesirable sliding back-and-forth of the caulk tube within the gun. Additionally, because of the distance between the front plate and back plate, only caulk tubes of a pre-determined size would fit in the caulk gun and not larger caulk tubes which hold more caulk. Furthermore, because the consumer market for caulk guns is very competitive, it is desirable to eliminate unnecessary materials, and their associated costs, in order to provide a more competitive product. The back plate, front plate, and intermediate frame structure are, in light of the present invention, unnecessary material and therefore add unnecessary expense to the caulk gun. And, smaller guns, i.e., not having a barrel or frame, would be more portable and more easily stored when not in use.